Isildur learned from Amandil that King Ar-Pharazôn, under the influence of Sauron, purposed to cut down Nimloth. One night Isildur went in disguise to Armenelos and from the courts of the King stole a fruit from the tree before it was cut down, thus preserving the line of the White Tree. It is said that he received grievous wounds from the King's guards before escaping but that they all healed when a leaf first appeared on the sapling that grew from the fruit he had taken.[2]

When Ar-Pharazôn ordered the Great Armament to assail the land of Aman, Elendil and his sons prepared ships to escape from Númenor. In the ship of Isildur was guarded the young White Tree.[2] When the Downfall of Númenor came in 3319[3] Elendil and his son escaped in nine ships – four for Elendil, three for Isildur, and two for Anárion.[2]

In the great storm that came with the drowning of Númenor the nine ships of the Exiles were borne to the east and scattered. Elendil was cast up in the land of Lindon, passed up the River Lhûn, and founded the realm of Arnor. Isildur and Anárion were carried to the south. Arriving at the mouths of the Anduin, they ascended the great river and founded the realm of Gondor.[4]

Isildur set up his house in Minas Ithil, where he planted the White Tree, while Anárion established his household in Minas Anor. However, they jointly ruled the kingdom and set up thrones side by side in the Great Hall of Osgiliath.[4] Isildur and his wife had two more sons, Aratan (in 3339) and Ciryon (in 3379), while living in Gondor.[1]

However, Sauron had also escaped the Downfall of Númenor. In S.A.3320, while the Exiles were establishing their realms, Sauron reentered Mordor and re-established his power. In 3429Sauron captured Minas Ithil and burnt the White Tree.[3] Yet Isildur escaped with his wife and sons, and a seedling of the White Tree. While Anárion held Osgiliath, Isildur and his family sailed down the Anduin, then northwest to Gil-galad in Lindon and his father in Arnor.[4]

The siege lasted seven years, but finally Elendil and Gil-galad threw down Sauron, thus winning the battle though both were slain and Elendil's sword Narsil broke under him as he fell. Isildur took the hilt shard of his father's sword and cut the One Ring from Sauron's finger. Ignoring the advice of Elrond and Círdan, lieutenant of Gil-galad, Isildur did not destroy the Ring; instead he claimed it as a weregild for the deaths of his father and brother, and an heirloom for his House. [4]

After the fall of Sauron, Isildur returned to Gondor and assumed the Elendilmir, proclaiming his Kingship in Arnor and sovereign lordship over the Dúnedain in both the North and the South. [5] He remained for a year in the South, planted the seedling of the White Tree in Minas Anor in memory of his brother Anárion, put the realm to order, and instructed his nephew Meneldil, son of Anárion, in the governance of the land. With Meneldil and a company of trusted friends, Isildur rode about the boundaries of Gondor and in Anórien created the tomb and memorial of Elendil upon the hill of Eilenaer, thereafter called Amon Anwar.[6] While he remained there, he wrote an account on how he acquired the Ring, its significance to his House and where he transcribed a verse around the Ring while it was still hot.[7]

When Isildur finally felt free to leave he committed the rule of Gondor to Meneldil and with his three sons departed on 5] Ivanneth, T.A.2. Instead of heading west and then north they journeyed northwards along the Anduin in order to first come to Imladris where his wife and little son Valandil were.[4] On the thirtieth day of the journey, 5Narbeleth, the King, his sons, and his Guard of two hundred knights and soldiers reached the northern borders of the Gladden Fields. Isildur believed that all soldiers of the Enemy perished so his camp was unguarded.[4] There they were ambushed by a band of Orcs said to be ten times their number.

As the Orcs closed in, Isildur sent his esquire Ohtar with one companion to fly with the shards of Narsil. The enemy charged and charged again. One by one Isildur's sons died about him; Elendur was the last and he insisted that Isildur leave with the One Ring. Isildur placed the Ring upon his finger and vanished from the battle.

The Orcs could still sense his smell[4] and Isildur ran to the Anduin and swam across the river. It was during this effort that the One Ring slipped from his finger. As he struggled to escape the reeds and rushes on the shore a small party of Orcs spotted him and shot him. He fell back into the water and no trace of him was found by Elves or Men.[5]

The line of Isildur continued, for Valandil became king of Arnor. Isildur's line continued unbroken throughout the Third Age until it formed the basis for Aragorn's claim to the kingship of Arnor and Gondor after the downfall of Sauron.[8]

In the riddling rhyme "Seek for the Sword that was Broken" the Ring is referred to cryptically as Isildur's Bane.[9]

After the War of the Ring the tower of Orthanc was opened, for King Elessar desired its restoration. Behind a hidden door in a steel closet was found Isildur's Elendilmir. It was surmised that Saruman had found the bones of the long-lost king and had taken the mithril fillet with its jewel for his own, possibly destroying the king's remains afterwards.[5]

Isildur briefly appears in the first scenes of the first film, as well as an extended flashback scene. Isildur is played by Harry Sinclair. Sinclair, a friend of Peter Jackson, was asked because he was the most corrupt looking person Jackson knew. Sinclair had only one line, "No!", which was dubbed by Hugo Weaving.

In the movie, Isildur apparently is the last king of Gondor; Anárion and heirs and Arnor do not appear at all. However, in the Extended Editions both Arnor and the House of Anárion are mentioned, and at times it is clear that Isildur was not the last King, so this might be dialogue error. The story of Isildur's succumbing to the temptation of the Ring bothers Aragorn who fears that he could have the same weakness (a fear that is not evident in the book).

In the game starts with a prologue, where you control Isildur on the slopes of Mount Doom. After you complete the mission you see how Isildur defeats Sauron. By completing the Tower of Orthanc bonus level, Isildur becomes a playable character in the other stages, where he takes the place of his descendant Aragorn. Strangely, Isildur's version of the "Tower of Orthanc" level has the same script as Aragorn's, leading to Saruman referring to the ancient King of Gondor as a "ragtag Ranger".

Isildur makes an appearance in a flashback scene titles "At the Stone of Erech". It covers the oath gives to Isildur by the men of Dunharrow, subsequent return of Sauron several years later, the betrayal of the Dunharrow men and the curse that Isildur lays upon them.